Get rid of ActiveModel::Configuration, make better use of
ActiveSupport::Concern + class_attribute, etc.

Support unicode character route directly in config/routes.rb. Fix #3470.

Before 7f4b0a1231bf3c65db2ad4066da78c3da5ffb01, this test are asserting
that update_attribute does the dirty tracking. Since we remove this
method and update_column write in the database directly this tests will
always fail>

Add uuid datatype support to PostgreSQL adapter

Remove update_attribute.

This reverts commit f5e7cb84.

Historically, update_attribute and update_attributes are similar, but
with one big difference: update_attribute does not run validations.
These two methods are really easy to confuse given their similar
names. Therefore, update_attribute is being removed in favor of
update_column.

See the thread on rails-core here:
https://groups.google.com/forum/?fromgroups#!topic/rubyonrails-core/BWPUTK7WvYA

This reverts commit d63b69ba.

framework

Bad Regexp exploits "fix" master branch

prevent users from unknowingly using bad regexps that can compromise security (http://homakov.blogspot.co.uk/2012/05/saferweb-injects-in-various-ruby.html)

This is the last chapter before I go back and make sure the guide is
complete/review

The `path` method on missing helper errors is inconsistent with the
implementation on LoadError in Ruby 2.0.  Wrap up the missing helper
exceptions so that the inconsistent behavior is mirrored in Ruby 2.0
(until we can figure out *why* it's inconsistent).

That change to update_attribute was considered
to be too subtle and was reverted in 30ea9230
just before Rails 3 shipped. Later we introduced
update_column (Rails 3.1).

These lines don't help to mitigate CVE. They only turn [nil] into nil, w...